An implantable medical device (IMD) such as an implantable cardioverter defibrillator (ICD) may be used to deliver shock therapy to a patient's heart in order to perform therapies such as defibrillation and cardioversion. Some ICDs may also provide several different pacing therapies, including such therapies as cardiac resynchronization, depending upon the needs of the user or patient and the medical condition of the patient's heart. For convenience, all types of implantable medical devices will be referred to herein as IMDs, it being understood that the term, unless otherwise indicated, is inclusive of an implantable device capable of administering any one of a number of cardiac therapies.
Typically, an IMD is implanted in a convenient location usually under the skin of a patient in the vicinity of one or more major arteries or veins. One (or more) electrical leads connected to the IMD is endocardially placed, usually through a convenient vein or artery. The ends of the leads are placed in contact with the walls or surface of one or more chambers of the heart, depending upon the particular therapy deemed appropriate for the patient.
One or more of the leads is adapted to carry a current from the IMD to the heart tissue to stimulate the heart in one of several ways, again depending upon the particular therapy being delivered. The leads are simultaneously used for sensing the physiologic signals provided by the heart to determine when to deliver a therapeutic pulse to the heart, and the nature of the pulse; e.g., a pacing pulse or a defibrillation shock. Such IMDs are typically housed in a container or can that is made of metal or some other conductive material.
In IMDs that deliver defibrillation or cardioversion therapies, it is necessary to develop high voltages, perhaps 750 volts or more, within the IMD in order to administer a sufficient shock to a patient to correct an arrhythmia or a fibrillation, particularly a ventricular fibrillation. To generate such high voltages, a battery and capacitors (usually two) may be used. Preferably, the capacitors are fully charged before defibrillation or cardioversion therapies are delivered. In some configurations, flyback and non-flyback transformers are employed to incrementally charge the defibrillation capacitors prior to therapy delivery. Once the capacitors are charged, the defibrillation or cardioversion therapy is delivered via insulated gate bipolar transistors or other suitable semiconductor switches that are switched on and off to apply charge stored in the capacitors in biphasic pulse waveform to the heart.
Because IMDs are implanted subcutaneously, it is preferable that the IMD is sized as small as possible to reduce any discomfort that the patient may experience post-implantation. Conventionally, however, some of the electronic components that are housed within the IMD are relatively large. For example, transformers are used which have coil and core members that are physically separate from other IMD components. Although these conventional transformers have been reliable, they consume a considerable amount of space within the IMD.
Accordingly, it is desirable to provide a method and apparatus for reducing the volume of an implantable medical device. In addition, it is desirable to decrease the size of a transformer for use in an implantable medical device, while maintaining its reliability. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.